CHARACTERIZATION OF FLY ASH BY X-RAY ANALYSIS METHODS

Techniques have been developed for quantitative determination of elemental and crystalline composition of fly ash by X-ray fluorescence and diffraction. In addition to being fast, the methods are accurate and the knowledge provided from quantitative crystalline composition explains many of the behavioral characteristics of fly ash. From the study on one Class C, cementitious fly ash it was found that 23 percent of its composition is crystalline and that significant amounts of aluminous cements (tricalcium aluminate and calcium aluminum sulfate) are present. The cements explain this fly ash's capability for high strengths after hydration. A study involving continuous X-ray diffraction monitoring of hydration products showed that both Ettringite and monosulfoaluminate were formed; but when sufficient quantities of gypsum were introduced, Ettringite formation became dominant. Free calcium oxide was also found in this fly ash, and its behavior with water suggests a hard burned form, which is a feature of particular importance to use of fly ash in Portland cement concrete.